compat: get rid of STRING_TYPES

I think it only obfuscates the code, also calling `bytes` a string type
is pretty misleading in Python 3.

src/_pytest/compat.py

@@ -181,9 +181,6 @@ def _translate_non_printable(s: str) -> str:
     return s.translate(_non_printable_ascii_translate_table)
 
 
-STRING_TYPES = bytes, str
-
-
 def _bytes_to_ascii(val: bytes) -> str:
     return val.decode("ascii", "backslashreplace")
 

src/_pytest/python.py

@@ -50,7 +50,6 @@ from _pytest.compat import is_generator
 from _pytest.compat import NOTSET
 from _pytest.compat import safe_getattr
 from _pytest.compat import safe_isclass
-from _pytest.compat import STRING_TYPES
 from _pytest.config import Config
 from _pytest.config import ExitCode
 from _pytest.config import hookimpl
@@ -998,7 +997,7 @@ class IdMaker:
     def _idval_from_value(self, val: object) -> Optional[str]:
         """Try to make an ID for a parameter in a ParameterSet from its value,
         if the value type is supported."""
-        if isinstance(val, STRING_TYPES):
+        if isinstance(val, (str, bytes)):
             return _ascii_escaped_by_config(val, self.config)
         elif val is None or isinstance(val, (float, int, bool, complex)):
             return str(val)

src/_pytest/python_api.py

@@ -24,7 +24,6 @@ from typing import TypeVar
 from typing import Union
 
 import _pytest._code
-from _pytest.compat import STRING_TYPES
 from _pytest.outcomes import fail
 
 
@@ -721,15 +720,10 @@ def approx(expected, rel=None, abs=None, nan_ok: bool = False) -> ApproxBase:
     elif (
         hasattr(expected, "__getitem__")
         and isinstance(expected, Sized)
-        # Type ignored because the error is wrong -- not unreachable.
-        and not isinstance(expected, STRING_TYPES)  # type: ignore[unreachable]
+        and not isinstance(expected, (str, bytes))
     ):
         cls = ApproxSequenceLike
-    elif (
-        isinstance(expected, Collection)
-        # Type ignored because the error is wrong -- not unreachable.
-        and not isinstance(expected, STRING_TYPES)  # type: ignore[unreachable]
-    ):
+    elif isinstance(expected, Collection) and not isinstance(expected, (str, bytes)):
         msg = f"pytest.approx() only supports ordered sequences, but got: {expected!r}"
         raise TypeError(msg)
     else: